Known scissor suspensions provide multiple advantages over straight linear suspensions. Such scissor suspensions are mentioned in various patent documents: U.S. Pat. No. 4,856,763, US 2010/0133413, U.S. Pat. No. 4,913,482, U.S. Pat. No. 5,169,112, U.S. Pat. No. 4,943,037, U.S. Pat. No. 5,927,679, U.S. Pat. No. 5,364,060, U.S. Pat. No. 5,975,508, U.S. Pat. No. 5,984,410 and U.S. Pat. No. 6,264,163. In addition, some patent documents relate to scissor suspension mechanisms: US 2007/0295882, US 2008/0156960, U.S. Pat. No. 3,853,296 and U.S. Pat. No. 5,222,709.
Known mechanisms have a scissor geometry by including a base frame, an upper frame in space relation and movable with respect to the base frame, and two crossed arms rotatably mounted on central pivots, the crossed scissor arms extending from the base frame to the upper frame and being free to rotate relative to one and other to selectively bringing the upper frame closer to and farther away from the base frame. Mechanisms may further include a pair of side members that can be linked by one or a plurality of torsional stiffeners, to cooperate with the crossed arms. Typically, mechanisms further include various pivots attached to either the base or upper frame for allowing horizontal movement thereof.
Some scissor suspension mechanisms have been designed to reduce their overall external dimensional properties. U.S. Pat. No. 3,853,296 is directed to reduce the overall height of the lowest position of the upper frame with respect to the base frame. Such a height reduction is obtained by misalignment of the central pivots along a vertical direction. The vertical misalignment allows horizontal alignment of pivots meaning a significant gain in vertical compactness. U.S. Pat. No. 7,517,018 also discloses a scissor suspension mechanism achieving height compactness in the lowest position of the upper frame. However, known scissor suspensions achieving height compactness in the lowest position of the upper frame may have a reduced elevation range and/or enlarged external side dimensions.
In the field of railroad freight and transit, efficiency of suspensions may be an important issue due to whole body vibration. In addition, suspension mechanisms having reduced external dimensions may be required in order to offer space for legs and/or general circulation around the seat. Typical height requirement between the cushion and the floor is 16 inches at the minimum adjustment with 4 inches for adjustment upwards. Therefore, in order to keep effective suspension for different seat height adjustments, scissor mechanisms have to be provided with a total elevation stroke of about 8 inches which will permit the seat cushion to be set from about 16 to 20 inches high while keeping the suspended mass in any height set up 2 inches away from mechanical limits.
Other patent documents known to the applicant include: US 2004/0144906, US 2006/0255639, US 2010/0117428, U.S. Pat. No. 4,382,573, U.S. Pat. No. 5,584,460, U.S. Pat. No. 5,794,911, U.S. Pat. No. 5,950,977, U.S. Pat. No. 5,957,426, U.S. Pat. No. 5,984,410, U.S. Pat. No. 655,074, U.S. Pat. No. 6,616,117, U.S. Pat. No. 6,776,384, U.S. Pat. No. 6,935,693, U.S. Pat. No. 7,044,553, U.S. Pat. No. 7,152,839, U.S. Pat. No. 7,185,867, U.S. Pat. No. 7,338,126, U.S. Pat. No. 7,413,158, U.S. Pat. No. 7,568,675, U.S. Pat. No. 7,669,823, U.S. Pat. No. 7,896,369.
Therefore, there is a need for a scissor suspension mechanism that has minimized external side dimensions while keeping maximized elevation stroke along with enhanced compaction capacity.